Generally, a refrigerating cycle or heat pump cycle using CO2 as a refrigerant is composed by connecting a compressor, gas cooler, pressure reducing device, and evaporator.
The gas cooler is a heat waster in the cycle in which, for example, water is heated and supplied as hot water. CO2 refrigerant has zero ozone depleting coefficient and its greenhouse effect index is 1, so it has advantages that it is environment-friendly, non-toxic, non-flammable, safe and cheap. A heat pump cycle using CO2 refrigerant is superior in efficiency in supplying hot water.
However, when the temperature of the water supplied to the gas cooler rises, the coefficient of performance (COP) of the cycle decreases.
A means to solve this problem is disclosed in patent literature 1 (JP-A-2003-194433). According to the means disclosed in patent literature 1, a heat exchanger is provided parallel to the open/close valve provided between the gas cooler and expansion valve, a temperature sensor is provided at the entrance of water of the gas cooler, and the open/close valve is closed when the temperature detected by the temperature sensor rises higher than a prescribed temperature. The heat exchanger is united with the evaporator in one or disposed separately and utilizes the latent heat of vaporization of the refrigerant in the evaporator to cool the refrigerant flowed out from the gas cooler.
When the open/close valve is closed, the refrigerant flowing out from the gas cooler bypasses through the open/close valve and flows into the heat exchanger provided parallel to the open/close valve, the refrigerant is cooled there, and the refrigerant fallen in temperature is introduced to the expansion valve to be expanded and introduced into the evaporator.
In the means disclosed in patent literature 1, as mentioned above, a heat exchanger is provided in order to lower the outlet side refrigerant temperature when the temperature of the water supplied to the gas cooler has risen higher than a prescribed temperature, that is, the refrigerant flowing out from the gas cooler is cooled by heat exchange within the CO2 heat pump cycle. By this method, the heat of the refrigerant flowing out from the gas cooler is dissipated uselessly to outside without utilizing the heat effectively. Further, this method can be applied only to a hot water supply system using a heat pump, and application is restricted.
On the other hand, due to the characteristics of the CO2 refrigerant, in the case the hot water heated in the gas cooler is used for a heat source to other equipment for room heating, etc. and the water returned from the other equipment is introduced to the gas cooler as cooling water, the returned water is rather high in temperature and coefficient of performance (COP) of the heat pump decreases.